One conventional type of fastener includes two substantially identical fastener members that each have a base and a plurality of headed stems adjoining and projecting from the base. The fastener members, and hence the objects to which the fastener members are attached, may be releasably fastened to each other by compressively engaging the fastener members. Fasteners of this type are advantageous because the engagement force is relatively small and the disengagement force, due to the interference between the respective headed stems, is relatively large.
A conventional fastener of the type described above is illustrated in FIG. 7. The fastener includes a first fastener member 1 and a second fastener member 2, each of which is integrally molded from a polymeric material. The first and second fastener members are provided with generally flat bases 3 and 4, respectively, and a plurality of headed stems 5 arranged on the bases in a predetermined spaced relationship. Each of the headed stems 5 has a stem 6 projecting generally orthogonally from the base and head 7 formed at the end of the stem 6. Each head has a diameter at at least one location that is greater than the diameter of the stem. The head 7 of each headed stem 5 has a generally flat engaging surface 8 adjacent to the stem 6 and extending radially outward from the periphery of the stem 6, and a curved apex 9 at an opposite side of the bottom surface 8.
The first fastener member 1 and the second fastener member 2 are positioned so that the bases 3, 4 are arranged substantially parallel to each other while the headed stems 5 thereof being mutually opposed, as shown in FIG. 7(a). In this position, when a predetermined compressive force is applied to the respective bases, the heads 7 of the headed stems 5 of one fastener member come into contact with and slide against, at the apexes thereof, the heads 7 of the headed stems 5 of the other fastener member. The stems 6 of the headed stems 5 of both fastener members deflect, and heads of each fastener member thus enter into a space between the headed stems 5 of the other fastener member, as shown in FIG. 7(b). The headed stems 5 of one fastener member are engaged, at the engaging surfaces 8, with the engaging surfaces 8 of the other fastener member. In this manner, the first fastener member 1 of the second fastener member 2 are attached to each other.
The conventional interengaging fasteners discussed above are preferably attached to each other by the mutual agreement of all of the headed stems. However, the fastener members can be attached even when only some of headed stems in the respective fastener members are engaged with each other. Accordingly, this type fastener has an advantage in that two independent articles can be attached with each other in any positional relationship. Furthermore, the base of the fastener member can be fixed to the article by using an adhesive tape or the like, the appearance of the articles is not injured.
For some fastening applications, the fastener members are not visible to the operator when the fastener is engaged. These applications are referred to as "blind" fastening applications, and an example of such a blind fastening application is shown in FIG. 8. FIG. 8 illustrates the case of applying a ceiling liner to the interior roof of an automobile. Three fasteners are shown, and those fastener members are not visible to an operator who is installing the ceiling liner. Because the operator cannot see whether and to what degree the fasteners interengage, the first fastener member 1 and the second fastener member 2 can be attached with each other even when only a part of the headed stems of both fastener members are mutually engaged, as shown in FIG. 8(b). This misalignment can result in inaccurate or weak installation, which may detract from both the appearance and the function of the ceiling liner.
If the fastener connecting process is performed by a robot, it may also be desirable to provide a fastener that may be engaged only when the fastener members are within a specified distance of each other, to insure that the fastener members are securely connected. This would allow robots that lack precision to satisfactorily engage the fastener. For example, if one fastener member has an area of 5 cm.sup.2 and a second fastener member has an area of 10 cm.sup.2, it may be desirable to permit engagement by the robotic apparatus only when the entire area of the first fastener member is engaged with the second fastener member.
In view of the foregoing, it would be desirable to provide a fastener comprising fasteners members of the general type described above, and further including structure for locating one fastener member with respect to the other fastener member, even if neither fastener member is visible to an operator. It is also desirable to provide a fastener comprising two fastener members having a specified range of acceptable interengagement positions.